The present invention relates to a passive optical network (PON) system including an optical line terminal (OLT) and optical network units (ONUs). More particularly, the present invention relates to an optical network system without loss of multicast signals and to a method of changing encryption keys.
In recent years, the PON system has been widely used as an optical access system in providing broadband Internet access service to subscribers. The PON system includes an OLT, plural ONUs, and an optical fiber. The OLT and the ONUs are connected through an optical splitter to form a star network topology.
ITU-T Recommendation G.984.3, “Gigabit-capable Passive Optical Networks (G-PON): Transmission convergence layer specification” specifies the ONU-initiated encryption method and encryption key sharing method for unicast communication between OLT and ONU.
The methods include the following steps: a first step in which the OLT transmits an encryption key generation request to the ONU; a second step in which the ONU generates an encryption key; a third step in which the ONU transmits three times the generated encryption key to the OLT; a fourth step in which the OLT performs an error check on the encryption key received three times from the ONU; a fifth step in which the OLT transmits a positive confirmation response to the ONU; and a sixth step in which the OLT makes a notice of timing of changing the encryption key.
The unicast communication is designed to change the encryption key by the above steps to increase the confidentiality of information.
In the encryption method for a multicast signal such as an IP video signal in the PON system, the optical signal is physically split by an optical splitter in an optical distribution network (ODN) between an OLT and ONUS. Thus, a non-multicast signal can be tapped between the ONUS sharing an optical fiber connecting the OLT and the optical splitter. This problem has been solved in JP-A No. 343243/2004.
JP-A No. 343243/2004 discloses an OLT-initiated multicast encryption key distribution method in which the OLT stores, manages, and distributes a multicast encryption key for each Internet group management protocol (IGMP) group.
JP-A No. 074168/2007 discloses an encryption key change method for changing an encryption key when the key sharing and member leave a group in multicast communication.